Kaon experiments at CERN: NA48 and NA62

TL;DR

This paper reviews kaon decay experiments at CERN, highlighting precise measurements of decay ratios, improved limits on lepton number violation, and future plans for ultra-rare decay studies, advancing tests of the Standard Model.

Contribution

It reports new precise measurement of the $R_K$ ratio, improved limits on lepton number violating decays, and outlines future goals for rare decay measurements at CERN.

Findings

Measured $R_K$ with high precision, consistent with Standard Model

Set improved upper limit on lepton number violating decay

Outlined future plans for ultra-rare decay measurement

Abstract

Searches for violation of lepton flavour universality and lepton number conservation in kaon decays by the NA62 and NA48/2 experiments at CERN, status and future plans of the CERN kaon programme are presented. A precision measurement of the helicity-suppressed ratio $R_K$ of the $K^\pm\to e^\pm\nu$ and $K^\pm\to\mu^\pm\nu$ decay rates has been performed using the full data set collected by the NA62 experiment in 2007--2008. The result is $R_K=(2.488\pm0.010)\times10^{-5}$, in agreement with the Standard Model expectation. An improved upper limit on the rate of the lepton number violating $K^\pm\to\pi^\mp\mu^\pm\mu^\pm$ decay from the NA48/2 experiment (2003--2004 data set) is presented. Finally, the NA62 project aiming at a measurement of the branching ratio of the ultra-rare decay $K^+\to\pi^+\nu\bar\nu$ at 10% precision is discussed.